Binary Tree Postorder Traversal

Problem

Given the root of a binary tree, return the postorder traversal of its nodes' values.

Solution Approach

Expected Time complexity: $O(n)$

Click - to see solution code

C++

class Solution {
    vector<int> postorder;

   public:
    void traversal(TreeNode* root) {
        if (!root) return;
        traversal(root->left);
        traversal(root->right);
        postorder.push_back(root->val);
    }

    vector<int> postorderTraversal(TreeNode* root) {
        traversal(root);
        return postorder;
    }
};